1. Field of the Invention
The present invention relates to a medical system and an antenna switching method, and more particularly to a medical system and an antenna switching method in and by which a capsule type medical apparatus introduced into a subject such as a person, an animal, and the like executes a wireless communication with an external machine disposed outside of the subject.
2. Description of the Related Art
In, for example, a medical field, a swallow-type capsule type medical apparatus has conventionally existed which has an information acquisition function for obtaining various kinds of information in a subject by being introduced into the subject such as a person, an animal, and the like and a wireless communication function for transmitting and receiving the obtained information, a control signal from an outside, and the like through a wireless line (refer to, for example, Japanese Application Patent Publication No. 2007-195961, Japanese Application Patent Publication No. 2007-175448, Japanese Application Patent Publication No. 2005-13338).
In a medical system using the capsule type medical apparatus as described above, a coil antenna (also called a loop antenna) is often used as a transmission/receiving antenna contained in the capsule type medical apparatus (refer to, for example, a paragraph 0039 of Japanese Application Patent Publication No. 2007-195961). This is because the coil antenna has a large gain in small antennas.
In contrast, the transmission/receiving antenna on an external machine side is ordinarily disposed in intimate contact with or close to the subject to improve a reception sensitivity of a radio wave radiated from the capsule type medical apparatus in the subject. Further, to permit a movement of the subject in a state that an antenna of the external machine is attached to the subject, the antenna of the external machine is ordinarily portably attached to the subject (refer to, for example, a paragraph 0027 or FIG. 1 of Japanese Application Patent Publication No. 2007-195961, for example, a paragraph 0021 or FIG. 1 of Japanese Application Patent Publication No. 2007-175448, or a paragraph 0035 or FIGS. 1 and 4 of Japanese Application Patent Publication No. 2005-13338). Thus, in general, an antenna having a simple configuration such as a dipole antenna, a loop antenna, and the like has been conventionally used as the antenna on the external machine side in consideration of portability and the like for the subject.
However, ordinarily, the coil antenna used as an antenna for the capsule type medical apparatus has directionality. Further, the dipole antenna or the loop antenna used as an antenna for the external machine also has directionality.
Here, FIGS. 1A and 1C show a relation between a mutual position and a reception strength (reception strength position dependence) obtained by an experiment for receiving a radio wave radiated from a coil antenna by a dipole antenna. FIG. 1A shows the reception strength position dependence to a vertical polarized wave when a coil antenna is disposed so that a winding axis is horizontal to the ground surface, and FIG. 1C shows the reception strength position dependence to a horizontal polarized wave when the coil antenna is disposed so that the winding axis is vertical to the ground surface likewise. Further, FIG. 1B shows a conceptual view showing a positional relation between a transmission antenna (coil antenna) and a reception antenna (dipole antenna) to explain the reception strength position dependence of FIG. 1A, and FIG. 1D shows a conceptual view showing the positional relation between the transmission antenna (coil antenna) and the reception antenna (dipole antenna) to explain the reception strength position dependence of FIG. 10. Note that, as shown in FIGS. 1B and 1D, respectively, the reception strength position dependency properties shown in FIG. 1A and FIG. 10 were obtained from a result of measurement of a strength of a radio wave received by a dipole antenna 1003 using a spectrum analyzer in a state that a coil antenna 1002 having a diameter of 3 mm was introduced into a cylindrical liquid phantom (simulated human body) 1001 having a diameter of 300 mm and a height of 300 mm and further the dipole antenna 1003 was caused to come into intimate contact with a side surface of the liquid phantom 1001. Note that a distance between the transmission antenna (coil antenna 1002) and the reception antenna (dipole antenna 1003) at the time was assumed to be 150 mm. Here, the vertical polarized wave is a radio wave, in which an electric field travels on a surface vertical to the ground surface and is a polarized wave which travels on a surface vertical to a winding axis of the coil antenna 1002 in FIG. 1B. Further, the horizontal polarized wave is a radio wave, in which an electric field travels on a surface horizontal to the ground surface, and is a polarized wave which travels on a surface vertical to the winding axis in FIG. 1D.
It can be found that although an approximately constant reception strength can be obtained as to a horizontal polarized wave of a radio wave radiated from the coil antenna 1002 regardless of a mutual position between the coil antenna 1002 and the dipole antenna 1003 as shown in FIG. 1C, a reception strength is outstandingly deteriorated (or reduced to 0) as to a vertical polarized wave when the dipole antenna 1003 is positioned in a horizontal direction to the coil antenna 1002 as shown in FIG. 1A. It can be found from what is described above that although the coil antenna does not have directionality as to the horizontal polarized wave, the coil antenna has directionality as to the vertical polarized wave.
Accordingly, in a medical system, which uses a coil antenna as a transmission/receiving antenna of a capsule type medical apparatus and uses a dipole or loop antenna as a transmission/receiving antenna of an external machine as in a conventional medical system, the transmission/receiving sensitivity is deteriorated depending on a positional relation between the antenna of the capsule type medical apparatus and the antenna of the external machine and data may not be accurately transmitted and received between the capsule type medical apparatus and the external machine.